There is an increasing market demand in customer segments like Public Safety and Homeland Security for outdoor, metropolitan-area broadband networks supporting vehicular mobility. The ubiquity, availability and low cost of 802.11-based devices are clear motivations for the use of 802.11 in such scenarios. However, the IEEE 802.11 OFDM physical layer was designed primarily for indoor wireless local area networks. Typically, 802.11 radios suffer greatly reduced performance or may fail completely when deployed in scenarios for which they were not intended such as outdoor, non-line-of-sight scenarios. Vehicular speed mobility further adds to difficulties applying 802.11 systems for outdoor use.
There are two main physical layer impediments for the application of 802.11 OFDM in outdoor mobile scenarios. The first impediment is that longer multipath delay spreads are typically encountered in outdoor channels. This causes self-interference via inter-symbol interference (ISI) and inter-carrier interference (ICI). The longer delay spread also increases the frequency selectivity of the channel, which causes difficulties with channel estimation. The second impediment is due to mobility, which adds the further complication that the multipath propagation effects are time-varying and may change appreciably within the duration of a single OFDM packet. Each of these effects can be present independently and are individually challenging. When present simultaneously, they pose significant difficulties for receiver design.
Our previous PCT application PCT/AU2007/000231, claiming priority from Australian provisional patent application no 2006900984, filed 27 Feb. 2006 and titled “Method and System for Communication in a wireless network”, the contents of which are incorporated herein by reference, discloses systems and methods for addressing at least one of the drawbacks of the prior art. The preferred embodiments described herein provide an alternative to the systems and methods disclosed in that specification.